Filters for extracting water vapors from a gas, a process known as drying, are very common and in widespread use at the present time. A common material employed is molecular sieve, a bead-like material made from diatomaceous earth with a very high surface area to volume ratio and an affinity for adsorbing water molecules.
Several design considerations apply to the construction of a successful desiccant filter assembly. The desiccant material must be closely packed in its container so that further settlement does not produce channeling or create voids where the gas can bypass close contact with the desiccant.
If the desiccant is exposed to vibrations in service it must be tightly packed to prevent the desiccant beads from rubbing against each other and against the walls of the container which can cause the material to breakdown and form dust.
If the desiccant is contained in a renewable cartridge the cartridge must be mounted in such a manner that it will not vibrate loosely in the housing for the cartridge. Also, the arrangement must be such that the wet inlet gas is prevented from mixing with and contaminating the dry discharge gas.
The gas flow must be directed from one end of the bed to the other and evenly distributed for effective use of all the desiccant material. The desiccant must be protected from direct contact with liquid water as that may cause it to disintegrate.